The present invention relates to a stencil printing machine and a method, and more particularly, to a stencil printing machine having two sets of printing sections in each of which a print medium is transferred through a path between a printing drum which carries thereon a stencil sheet and a pressure rotary member which is provided to the associated printing drum for thereby selectively carrying out a printing operation in a both sides printing mode and in a one side printing mode, and to a method of selectively carrying out a printing operation in a both sides printing mode and in a one side printing mode.
A stencil printing machine that enables a both sides printing operation with the use of two sets of printing sections is shown in FIG. 7. FIG. 7 shows an overall structure of the stencil printing machine for the both sides printing operation.
In FIG. 7, the stencil printing machine 100 is constructed of upstream and downstream stencil making sections 104, 105 with respective thermal printing heads 102, 103 for thermally perforating respective stencil sheets 101, 101 on the basis of respective image data, an upstream printing section 109 wherein the stencil sheet 101 made in the upstream stencil making section 104 is mounted onto an upstream printing drum 106 and a print sheet 107, which is fed thereto, is transferred through a path between the upstream printing drum 106 and a press roller 108 in a pressured contact relationship to transfer ink onto an upper surface (one surface) of the print sheet 107 during such a transfer step, a paper feed section 110 which feeds the print sheet 107 to the upstream printing section 109, an upstream belt-conveyer transfer unit 111 located at a sheet discharge side of the upstream printing section and transferring the print sheet 107 to a downstream side with the action of a belt 121, a downstream printing section wherein the stencil sheet 101, which is made in the downstream stencil making section 105, is mounted onto a downstream printing drum 112 and the print sheet, which is fed from the upstream belt conveyer transfer unit 111, is transferred through a path between the printing drum 112 and a press roller 114 in a pressured contact relationship to transfer ink onto a lower surface (the other surface) of the print sheet 107 during such a transfer step, and a downstream belt-conveyer transfer unit 117 with a belt 122 located at a sheet discharge side of the downstream printing section 115 for transferring the print sheet 107 to a sheet discharge tray 116 located in a downstream side.
Further, the upstream and downstream printing sections 109, 115 include squeegee rollers 123, 123 located inside the printing drums 106, 112, respectively, and held in contact with inner surfaces of outer peripheral walls 106a, 112a of the respective printing drums 106, 112, doctor rollers 124, 124 located in close proximity to the squeegee rollers 123, 123, respectively, to form respective given gaps relative thereto, and ink supply units 125, 125 each for supplying ink to an each area between the rollers 123, 124, with the squeegee rollers 123, 123 being arranged to rotate on inner peripheral surfaces of the outer peripheral walls 106a, 112a in association with rotations of the respective printing drums 106, 112. In addition, as the squeegee rollers 123, 123 rotate with, the rotations of the printing drums 106, 112, the outer peripheral surfaces of the squeegee rollers 123, 123 are adhered with ink in a given film thickness, with the adhered ink being.transferred to the outer peripheral walls 106a, 112a to allow ink to be supplied to an inner side of the print sheet 101 at all times.
Now, the both .sides printing operation is described below. Rotations of the printing drums 106, 112 allow the print sheet 107 to be fed from the paper feed section 110 to the upstream printing drum 106 in synchronism with the rotation thereof. The print sheet 107, thus fed to the printing drum 106, is brought into pressured contact with the stencil sheet 101 of the printing drum 106 with the press roller 108 to allow ink image to be transferred onto the upper surface of the print sheet 107, with the print sheet 107, whose upper surface is printed, being peeled off from the outer peripheral wall of the printing drum 106 and being introduced to the upstream conveyer-belt transfer unit 111. The upstream belt-conveyer transfer unit 111 causes the belt 121 to move for transferring the print sheet 107 with its lower surface remaining contact with the belt, thereby feeding the print sheet 107 from the most downstream side of the belt 121 to the downstream printing drum 112. The print sheet 107, thus fed to the downstream printing drum 106, is then brought into pressured contact with the stencil sheet 101 of the printing drum 112 with the press roller 114 to transfer ink image onto the lower surface of the print sheet 107, with the print sheet 107, whose lower surface is printed, being peeled off from the outer peripheral wall of the printing drum 112 to be introduced to the downstream belt-conveyer transfer unit 117. The downstream belt-conveyer transfer unit 117 causes the belt 122 to move for transferring the print sheet 107 from the most downstream side of the belt 122 to the sheet discharge tray 116. The print sheet 107 thus discharged to the sheet discharge tray 116 is placed therein in the stacked state.
Also, such a stencil printing machine is disclosed in Japanese Patent Application Laid-Open Publication No. 8-90893.
In the aforementioned stencil printing machine for the both sides printing operation, it is desired to achieve a one side printing operation and, so, various attempts have been conducted in the related art. For example, one technology to achieve this end concerns the two printing drums 106, 112, one of which is mounted with a stencil sheet 101 which is perforated on the basis of image data, and the other one of which is mounted with a non-perforated stencil sheet 101. With such arrangement, when executing the printing operation in the same manner as the both sides printing operation, the print sheet is transferred with ink at the printing section mounted with the perforated stencil sheet 101 whereas the print sheet is not transferred with ink at another printing section mounted with the non-perforated stencil sheet 101, thereby achieving the one side printing operation.
An alternative approach to achieve the one side printing operation is to locate a transfer unit at the discharge side of the upstream printing section 109 to transfer the print sheet 107 in another route to the sheet discharge tray without directing the print sheet 107 to the downstream printing section 115. With such a structure, during the one side printing mode, the print sheet 107, which is printed in the upstream printing section 109, is discharged in another route, thereby achieving the one side printing operation.
However, in the former one side printing technology, the presence of the need for mounting the non-perforated stencil sheet onto one of the printing drums induces the waste of the stencil sheets. In the latter one side printing technology, the presence of the need for additionally locating the transfer unit as an extra printing drum mechanism in another route specific for the one side printing operation is a major cause of an inherent large size in structure and an increase in manufacturing cost.
Since, further, the two printing drums 106, 112 must be rotated in synchronism with one another while retaining a given rotational angular phase difference, it is a usual practice to employ a single drive source for rotating both of these printing drums. Accordingly, if the printing drum 106 (or 112), which is not in charge of the one side printing operation, is rotated, this rotation of the printing drum causes the squeegee roller 123 remaining inside the printing drum to rotate, with a resultant undesired continuous operation of the squeegee roller 123 to supply ink to the outer peripheral wall 106a (or 112a) of the printing drum 106 (or 112). Since, however, this ink is not transferred to the print sheet 107 and is merely subjected to an undesired kneaded result, another problem is encountered in that an excessive amount of kneading frequencies of ink results in deterioration of quality.
The present invention has been made in view of the above studies and has an object to provide a stencil printing machine and a method for performing a printing operation which enable a one side printing operation without causing the waste of stencil sheets, without providing a transfer mechanism in another route for the one side printing operation and also without causing deterioration in the quality of ink.
According to one aspect of the present invention, there is provided a stencil printing machine selectively carrying out a printing operation in a both sides printing mode and in a one side printing mode, which comprises: an upstream printing section including a first printing drum formed with an ink permeable outer peripheral wall adapted to be mounted with a stencil sheet, a first ink supply unit supplying ink to an inner periphery of the first printing drum, and a first press rotary member operative to be held in a pressured position in contact with the outer peripheral wall of the first printing drum to allow ink to be transferred onto one surface of a print medium; a downstream printing section including a second printing drum formed with an ink permeable outer peripheral wall adapted to be mounted with a stencil sheet, a second ink supply unit supplying ink to an inner periphery of the second printing drum, and a second press rotary member operative to be held in a pressured position in contact with the outer peripheral wall of the second printing drum to allow ink to be transferred onto the other surface of the print medium; a paper feed section feeding the print medium to the upstream printing section; and a printing-drum drive escape mechanism operative to shift either selected one of the first and second printing drums into a drive escape position to interrupt rotation of the selected printing drum while retaining either selected one, associated with the selected printing drum, of the first and second press rotary members in a separated position to pass the print medium into a sheet discharge section along the selected printing drum without contact with the selected press rotary member, in the one side printing mode.
Besides according to the present invention, a method, which selectively carries out a printing operation in a both sides printing mode and in a one side printing mode, provides an upstream printing section including a first printing drum and a first press rotary member operative to shift between a pressured position and a separated position relative to the first printing drum; provides a downstream printing section including a second printing drum and a second press rotary member operative to shift between a pressured position and a separated position relative to the second printing drum; provides a printing-drum drive escape mechanism operative to enable a shift of either selected one of the first and second printing drums into a drive escape position; feeds a print medium to the upstream printing section; and feeds the print medium, which is discharged from the first printing drum of the upstream printing section, to the downstream printing section. Here, when the one side printing mode is selected, the printing-drum drive escape mechanism is operative to shift either selected one of the first and second printing drums to a drive escape position to render the selected printing drum inoperative and to render the selected press rotary member to remain in a separated position away from the selected printing drum to pass the print medium into a sheet discharge section along the selected printing drum without contact with the selected press rotary member, in the one side printing mode.